WASHINGTON, DC -- And so, rather astonishingly, here we finally are. Over the next few hours, the polls will close in the last two contests of this extraordinary primary season, and by the end of it -- as we've heard so incessantly from every TV talking head for months that it's hard to keep in mind that it's actually true -- history will have been, like, totally made. Either Barack Obama will have become the first African-American nominee in the history of the major parties, or... nope, there isn't an 'or', really. (Just because it's a historic night doesn't mean the outcome's in doubt.) That said, it may not be tidy, since Hillary Clinton's team have spent the day denying rumours that she'll officially concede tonight. As I write, the superdelegates are endorsing Obama at a fast clip, and he's now just 11.5 away from the total delegate figure of 2,118 that he needs to clinch the nomination. (My figures are from RealClearPolitics, and most other sources agree or nearly agree; the AP, using its super-secret estimate that it won't explain to anybody, says he's already made it.) Obama will be in St Paul, Minnesota, where he's cheekily holding a rally in the very venue where the Republicans will hold their convention later this year. But Poignancy Central tonight will undoubtedly be Baruch College in downtown Manhattan, where Hillary Clinton is expected to speak at some point tonight, and where we'll get the first hints of what her next move might be. (She has said, apparently, that she's "open" to being vice-president. Hey -- me too.) I'll be liveblogging here from the Guardian's Washington headquarters, with updates from Suzanne Goldenberg in St Paul and Ed Pilkington in New York, until such time as I decide to go to bed. In the meantime, pull up a chair, crack open a beer -- or even some Puerto Rican rum, which is what Hillary campaign chair Terry McAuliffe seems to be drinking live on television these days -- and please do leave your thoughts in the comments below (or email oliver.burkeman@guardian.co.uk).

7.25pm (all times Eastern) What to expect tonight

The primaries, as I seem to have failed to mention immediately above, are of course in Montana and South Dakota, with 31 delegates at stake; Obama should win Montana with little difficulty, but at least one recent South Dakota poll gave Clinton a significant lead. Not that the specific outcomes matter much at this point, but the timings will influence the choreography of tonight's events:

8pm: First South Dakota polls close. 9pm: Remaining South Dakota polls close, and the results begin. (Did you know that all ballot papers in South Dakota have to be driven to a central office in each county, rather than counted at the precinct level, potentially slowing things down? And don't you feel, somehow, better for knowing that?) Clinton might choose this point to address supporters in New York, before Obama (probably) sweeps Montana, setting off the last domino rally of superdelegates. 10pm. Polls close in Montana. Terry McAuliffe opens second bottle of rum.

7.30pm There is, of course, nobody from whom one wants to hear more on an evening such as this than Mr Karl Rove, who just said on Fox News that he thinks "it's plausible" that Clinton would prefer Obama to lose to McCain in November so that she can run in 2012.

7.35pm CNN reports that Obama needs just seven more delegates to reach 2,118.

7.46pm A scene-setter from Suzanne in St Paul:

The venue here is a circular stadium -- home to the Minnesota Wild hockey team -- and it's not that big; people have been queuing up to get in since 10 in the morning. Quite a few of them brought things to do: I saw people with playing cards, people playing blackjack... and a lot of families with parents in their 40s and 50s with children in their late teens... The timing is perfect for Obama tonight. The polls in Montana will close at 9pm Minnesota time -- he'll sweep Montana; Clinton didn't contest it and the networks will call it for him as soon as the polls close. Then he can come out and speak. The Obama campaign already know they've got the numbers.

Ed in New York meanwhile describes a "fairly cheerful" atmosphere in New York. Stiff upper lips are clearly not just the preserve of the British.

8pm. Obama now just 6 delegates away, according to CNN's count. (Nine or 10 according to other sources.)

8.03pm. For those who continue to express a frankly irrelevant and frivolous interest in what I'm eating while writing these liveblogs -- as if Major World Events weren't unfolding at the very same moment -- I will take this opportunity to mention that I am eating cheese-flavoured popcorn. Also, there is some beer in the fridge.

8.11pm. According to CNN's Mr Monotone, Wolf Blitzer, what's happening RIGHT NOW is that Barack Obama only needs four more delegates. RIGHT NOW. That's what's happening right now!

8.15pm. OK, screw it. Breaking news: I'm calling the nomination for Obama. That's right: me, acting in a strictly personal capacity. See how the major networks respond to that.

8.22pm. As Marc Ambinder points out, exit polls from Montana and South Dakota suggest a lower incidence than in previous contests of Clinton voters saying they'd favour McCain over Obama if that was the choice that confronted them in November. There may be state-specific demographic and cultural reasons for that -- or perhaps something's really changing in terms of unity within the party. [Correction: That's really only a fair reading of the South Dakota polls, and it's my reading, more than Ambinder's.]

8.28pm. When I spoke to Ed Pilkington in New York just now, I could barely hear him: mobile phone reception in the Baruch College gym (which I did manage to hear Ed describe as "not particularly glamorous") is so bad that the Clinton campaign saw fit to warn reporters about it in advance, and Andrea Mitchell on MSNBC just now described the venue as a "hermetically sealed chamber" with virtually no cellular or internet connection to the outside world (although to be fair the television feeds seem to be working). An odd decision if you want lots of (non-TV) media coverage for an event. Maybe Clinton doesn't...

8.37pm. Look who's elbowing in tonight in an attempt to get a bit of attention tonight: it's John McCain, about to address supporters in Louisiana. I think someone's feeling a little ignored.

McCain: "Tonight we can say with confidence that the primary season is over and the general election campaign has begun."

So there you have it.

8.39pm. McCain pays a few condescending compliments to Hillary Clinton ("I'm proud to call her my friend") before audaciously unveiling his brilliant and original new campaign platform: change. "No matter who wins this election, the direction of this country is going to change ... but the choice is between the right change and the wrong change. Between going forward and going backward." If you prefer good things to bad things, you know who to vote for! McCain promises to turn "challenges and opportunity into opportunities." Got that?

McCain is laying into the response to Hurricane Katrina: "Incompetence of government at all levels to meet even its most basic responsibilities." And now laying into Obama for clinging to old-fashioned big-government ideals. "That attitude created the unresponsive bureaucracies of big government in the first place. And that's not change we can believe in." I think that means Obama was to blame for Katrina. Or something.

8.59pm McCain's speech is a pretty strident one-by-one denunciation of Obama's policies or alleged policy positions ("that's not change we can believe in!"). But he needs to finish up quick, because Clinton will surely be coming on soon.

9.06pm Tom Brokaw on MSNBC just compared Obama's nomination to the first moon landing. "However you feel about him, this is a milestone in American politics." All the anchors are struggling to find the words, it seems (apart from Wolf Blitzer, who never really had them in the first place). Tim Russert: "Just put [this] into context of our nation, and the whole issue of race. It's breathtaking."

9.15pm: Here's Obama's chief strategist David Axelrod, and his moustache, and they're both looking almost comically thrilled. It's "a hugely gratifying evening for us... We believe when he steps on that stage tonight he'll be the presumptive nominee of the party." They're still playing that damn song in St Paul, though. The Obama campaign are predicting a total turnout of 19,000-20,000 in Minnesota.

9.20pm "I thought that McCain was utterly woeful," writes AmoryBlaine in the comments. "His bizarre, forced perma-grin reminded me of Gordon Brown..." Let me add to that: his tiny crowd was embarrassing compared to both the crowds we're seeing tonight for Obama and Clinton -- no shame in that, since it's not the Republicans' night tonight; there will be plenty of enormous Republican rallies in the coming months. But a very odd decision by McCain to seek the TV coverage tonight at all, surely?

Clinton is expected to speak any minute. Watch this space...

9.24pm CLINTON WINS! In South Dakota, that is. CNN, MSNBC and Fox all call it.

9.31pm Here are Hillary and Bill in New York, shaking hands with the crowds.

9.33pm And here it comes. "Thank you all so much... I want to start tonight by congratulating Senator Obama and his suppporters on the extraordinary race he has run. Senator Obama has inspired so many Amercians to care about politics, and inspired so many more to get involved... Tonight I would like all of us to take a moment for all of us to recognise him and all his supporters for all they have accomplished." Cheers -- I can't hear any jeers, anyhow.

I didn't hear it, but Ben JP in comments notes: "Hillary Clinton was just introduced as the 'next President of the United States'. Doesn't bode well for any hopes of a concession speech."

Clinton: "In the millions of quiet moments, in thousands of places, you asked yourselves a simple question: who will be the strongest candidate...? Who will be ready to take back the White House and take charge as Commander-in-Chief and lead our country to a better tomorrow? ... And on election day after election day, you came out in record numbers to cast your ballots. Nearly 18m of you cast your votes for our campaign, carrying the popular vote with more votes than any primary candidate in history." Well, there's certainly nothing concessionary in her tone so far. A mention of "the pundits and the naysayers" gets big jeers.

9.40pm. Positively aggressive chanting and cheering from the New York crowd. ("Yes she can! Yes she can!" Um...) "I often felt that each of your votes was a prayer for our nation... I am so proud we stayed the course together. Because we stood our ground it meant that every single United States citizen had a chance to make his or her voice heard."

9.43pm. "I understand that a lot of people are asking: 'What does Hillary want? What does she want? Well, I want what I have always fought for in this campaign: to end the war in Iraq, to turn the economy around, healthcare for every citizen..." Did you spot the clever rhetorical move there?

9.47pm. From Suzanne in St Paul:

So deep inside Obamaland here there is no sign that a) Hillary has actually won South Dakota by a big margin and that b) Clinton is speaking right at this moment. Instead, the jumbo screen is showing people waving signs to Stevie Wonder songs. Keith Ellison, the local Congressman -- the one who actually WAS sworn in on a Koran -- keeps walking the floor of the arena, getting a big cheer from the crowd as he does so.

Clinton is thanking people for praying for her and for gripping her arms.

9.49pm "Now the question is where do we go from here... it's a question I don't take lightly. This has been a long campaign and I will be making no decisions tonight."

She's urging everyone to "go to my website, HillaryClinton.com, and let me know your thoughts and help in any way you can." Gotta pay those debts... In the coming days she'll be be "consulting party leaders [on] how to move forward" with the party's best interests at heart.

9.51pm Heartfelt thanks to Chelsea and to Bill, who is looking radically pink tonight. I mean, really, really strangely pink. (From St Paul, Minnesota: "They just yanked Signed Sealed Delivered after a few bars, and went to I Feel Good. Does this mean they have got the jitters about Montana...?")

9.53pm A 9/11 reference. Ground Zero reminds Clinton of America's resilience. "There is nothing we can't do... if we just start acting like Americans again. Thank you all very much. God bless you, and God bless America." And that's all we're hearing from Hillary tonight. The song to play her out? Simply The Best. Some in the New York crowd, I'm told, were chanting 'Denver! Denver!'

10pm CNN calls Montana for Obama, if you're interested. The primaries are over.

10.07pm In St Paul, Barack and Michelle Obama arrive to greet the crowd. "Two young people from the south side of Chicago," as MSNBC describes them.

10.10pm. Crowd uproar, and here we go. First, Obama says "thank you" about 25 times -- I'm not kidding. Now he's thanking his grandmother "who's sitting in Hawaii somewhere, because she can't travel."

"Tonight, Minnesota, after 54 hard-fought contests, our primary season has finally come to an end. Sixteen months have passed since we first stood together on the steps of the old state capitol in Springfield, Illinois. Thousands of miles have been travelled. Millions of voices have been heard. And because of what you said -- because you decided that change must come to Washington; because you believed that this year must be different than all the rest; because you chose to listen not to your doubts or your fears, but to your greatest hopes and highest aspirations... Tonight we mark the end of one historic journey with the beginning of another -- a journey that will bring a new and better day to America. Because of you, tonight, I can stand here and say that I will be the Democratic nominee for President of the United States."

10.16pm And now it's time to thank and praise Clinton -- the crucial part that Obama needs to handle just right. It might not be a complete exaggeration to say his presidential hopes depend upon it. "Senator Hillary Clinton has made history in this campaign not just because she's a woman who has done what no woman has done before, but because she's a leader who inspires millions of Americans with her strength, her courage, and her commitment to the causes that brought us here tonight... We've certainly had our differences over the last 16 months. But as someone who's shared a stage with her many times, I can tell you that what gets Hillary Clinton up in the morning -- even in the face of tough odds -- is exactly what sent her and Bill Clinton to sign up for their first campaign in Texas all those years ago... what led her to the United States Senate and fueled her barrier-breaking campaign for the presidency: an unyielding desire to improve the lives of ordinary Americans, no matter how difficult the fight may be.

"And you can rest assured that when we finally win the battle for universal health care in this country -- and we will win that fight -- she will be central to that victory. When we transform our energy policy and lift our children out of poverty, it will be because she worked to help make it happen. Our party and our country are better off because of her. And I am a better candidate for having had the honor to compete with Hillary Rodham Clinton." Nicely done, so far, I'd say...

...Although that seems to be the last mention that Clinton's going to get. Certainly nothing even remotely specific referring to Clinton's possible role(s) in the immediate future of the Democratic party. And now we're on to John McCain.

"There are many words to describe John McCain's attempt to pass off his embrace of George Bush's policies as bipartisan and new. But change is not one of them. Change is a foreign policy that doesn't begin and end with a war that should've never been authorized and never been waged. I won't stand here and pretend that there are many good options left in Iraq, but what's not an option is leaving our troops in that country for the next hundred years..."

Thinking back to McCain's appearance earlier this evening, the contrast is just... mindboggling. That's not really fair, of course, inasmuch as the McCain campaign will muster big crowds down the line. But it does make you wonder how it's going to affect the general election campaign -- the way the candidates come across on TV, which means so much, after all -- if McCain's events end up seeming so underpowered.

10.29pm. "John McCain has spent a lot of time talking about trips to Iraq in the last few weeks, but maybe if he spent some time taking trips to the cities and towns that have been hardest hit by this economy -- cities in Michigan, and Ohio, and right here in Minnesota - he'd understand the kind of change that people are looking for." It's crucial, of course, for Obama to focus the campaign from here on in on the economy, just as McCain will want to focus it on security.

10.34pm And building to the big finale, via mentions of Gettysburg and Antietam and the Greatest Generation, and finally Selma...

America, this is our moment. This is our time. Our time to turn the page on the policies of the past. Our time to bring new energy and new ideas to the challenges we face. Our time to offer a new direction for the country we love. The journey will be difficult. The road will be long. I face this challenge with profound humility, and knowledge of my own limitations. But I also face it with limitless faith in the capacity of the American people. Because if we are willing to work for it, and fight for it, and believe in it, then I am absolutely certain that generations from now, we will be able to look back and tell our children that this was the moment when we began to provide care for the sick and good jobs to the jobless; this was the moment when the rise of the oceans began to slow and our planet began to heal; this was the moment when we ended a war and secured our nation and restored our image as the last, best hope on Earth. This was the moment -- this was the time -- when we came together to remake this great nation so that it may always reflect our very best selves, and our highest ideals. Thank you, Minnesota, God bless you, and may God bless the United States of America.

And so it begins.

10.40pm By the way, after a cluster of superdelegate pledges immediately after the closure of polls in Montana, Obama officially passed the 2,118 figure, so he now officially officially has the delegates.

10.58pm Here's Andrew Sullivan on the truly extraordinary difference between Obama's speech and McCain's. The Huffington Post, meanwhile, has video of Clinton's.

11.10pm There'll be plenty of analysis, over the next 24 hours and beyond, of what happened tonight -- you can start with Suzanne Goldenberg's look back at the Clinton campaign, and Ezra Klein's analogy to the bad BBC sitcom Coupling, which is, oddly, far more illuminating than it sounds. And Jesse Jackson's thoughts. So I'll leave it here for now, with this summary: Obama won. Clinton, for all her well-controlled tone, seemed to be on a different planet, as if nothing hugely significant had occurred; it remains to be seen, over the next few days, what scope she has for using this strategically in planning her next moves (what does she want?). McCain embarrassed himself: a tiny gathering, and a bad speech that would have been far better left un-given: it was halting, and tetchy, and in its refrain of "that's not change we can believe in" it seemed to be following an agenda set by the Obama campaign. (Democrats are presumably hoping tonight for more of the same.)

And the Democratic nominee for the presidency is the person we'd known it would be for several weeks -- a fact that doesn't render what happened in America tonight any less historic.